Merged r13130 from trunk to 2.5-stable

Gemfile: update Rails 3.2.18

git-svn-id: http://svn.redmine.org/redmine/branches/2.5-stable@13133 e93f8b46-1217-0410-a6f0-8f06a7374b81
Merge remote-tracking branch 'upstream/2.5-stable' into ro-2-5
Revert "workaround of Ruby 2.1.1 with Rails 3.2"

This reverts commit 08336eeb2267a73941054d64461f7d1e4ac3955e.
update Ruby 2.1.2 and dependencies